Discoloration-fast dispersion adhesives having a prolonged potlife

ABSTRACT

The present invention relates to water-resistant aqueous dispersion adhesives with prolonged pot life and good color constancy of their bonds, comprising homopolymeric and/or copolymers polyvinyl esters, polymeric protective colloids, water-soluble compounds which can be complexed with the polymeric protective colloids, and derivatives of glyoxal and polyaldehydes having at least 3 carbon atoms, from which aldehyde groups can be controllably released in acidic media. The inventive dispersion adhesives are suitable for adhesively bonding porous and semiporous substrates.

The present invention relates to water-resistant, polyvinyl ester-based,aqueous dispersion adhesives with a long pot life and good colorconstancy of their bonds on storage, to processes for preparing thesedispersion adhesives, and to their use for bonding porous and semiporoussubstrates.

Polyvinyl ester dispersions, whose films exhibit increased waterresistance, normally comprise reactive monomers or additives whichdecrease the hydrophilicity of the adhesive by crosslinking thepolyvinyl alcohol which is used for stabilizing the dispersion.Crosslinking additives of high efficiency which are employed inwater-resistant adhesive dispersions based on polyvinyl ester includesfree aldehydes or their adducts with nucleophiles, which are able toundergo crosslinking reactions either inherently or, following removalof masking agents, by way of reactive aldehyde groups that have beenreleased.

As crosslinking catalysts it is common to use hardener salts. Hardenersalts disclosed by U.S. Pat. No. 3,563,851 and DE-C-26 20 738 includespecific metal salts, examples being those of aluminum or those oftransition group elements with the oxidation states III or IV.

DEB-22 61 402 describes water-resistant adhesive bonds based on apolyvinyl ester dispersion to which a urea-formaldehyde resin withcrosslinking activity, in combination with a free organic or inorganicacid or an acidic metal salt, is admixed.

EP-A0 413 136 describes adhesives with cold water resistance based onpolyvinyl alcohol and polyvinyl esters. Crosslinking adducts usedinclude N-nucleophiles with glyoxal, examples being cyclic ureas orcopolymerized reaction products of acrylamide. Through the addition ofacidic metal salts, based preferably on aluminum, the water resistancecan be improved.

EP-B-0 686 682 describes aqueous dispersion adhesives of increased waterresistance, comprising homopolymeric or copolymeric polyvinyl esters,protective colloids, compounds which can be complexed with theprotective colloids, and at least partly masked polyaldehydes having alleast 3 carbon atoms which controlledly release aldehyde groups inacidic media. A subgroup of the complexible compounds is formed by metalsalts, aluminum salts or zirconium salts for example. The resultingadhesives give rise advantageously to pale gluelines and satisfyrelevant test standards, especially the DIN EN 204 durability classes D2and D3 (cold water resistance) and DIN EN 204 D4 (hot water resistance).The pot lives following admixture of the ingredients are at least 8hours.

For the end user of these adhesives, a long pot life, i.e., a slowincrease in the viscosity of the dispersion following activation withthe acidic metal salts, is fundamentally a desirable feature. Anotherdesirable feature is high color constancy of the pale gluelinesfollowing application. The use of transition metal salts or aluminumsalts as crosslinking catalysts has the disadvantage of a gradualdarkening of the gluelines, caused by the reaction of the metal saltswith polyvinyl alcohol or any substances contained in wood that may bepresent. The effect is observed on aging of the adhesive bond at roomtemperature, and is accelerated on exposure to heat.

One attempted solution to improving the discoloration of wood adhesivedispersions based on polyvinyl esters and comprising hardeners isdescribed by DE-A-196 49 419. According to DE-A-196 49 419, the additionof low molecular mass polyvinyl alcohols having Höppler viscosities offrom 2 to 6 mPa·s (measured in 4% strength aqueous solution) reduces thediscoloration tendency in the case of cold water resistant adhesivebonds of durability class D3. A disadvantage is that the addition ofsizable amounts of polyvinyl alcohol, which acts as a hydrophilicizingagent, decreases the hot water resistance of bonds.

The object accordingly was to provide polyvinyl ester dispersions foradhesives which possess a high, user-compatible pot life and whoseadhesive bonds exhibit high color constancy with a high level of waterresistance.

It has now surprisingly been found that aqueous dispersion adhesivescomprising at least

a) one homopolymeric and/or copolymeric polyvinyl ester,

b) one polymeric protective colloid,

c) one water-soluble compound which can be complexed with the polymericprotective colloids, and

d) two, at least partly masked polyaldehydes which release aldehydegroups again in acidic media, wherein at least one masked polyaldehydeis a glyoxal derivative and at least one other masked polyaldehyde is aderivative of a polyaldehyde having at least 3 carbon atoms,

feature a long, user-compatible pot life and a high level of waterresistance and color constancy of their gluelines.

The polyaldehydes having at least 3 carbon atoms are aldehydes having afunctionality of at least two.

Suitable monomeric units for the homopolymeric and copolymeric polyvinylesters include preferably vinyl acetate, vinyl formate, vinylpropionate, vinyl isobutyrate, vinyl pivalate, vinyl 2-ethylhexanoate,vinyl esters of saturated, branched monocarboxylic acids having 9 to 10carbon atoms in the acid radical, vinyl esters of relatively long-chain,saturated or unsaturated fatty acids such as, for example, vinyllaurate, vinyl stearate, and also vinyl esters of benzoic acid and/orsubstituted derivatives of benzoic acid such as, for example, vinylp-tert-butylbenzoate. Vinyl acetate is of particularly preferredsuitability.

The weight fraction of vinyl ester(s) in the copolymer of polyvinylesters is preferably at least 50% by weight and with particularpreference at least 75% by weight.

The copolymeric vinyl esters contain, where appropriate, as furthermonomer units

a) up to 50% by weight, preferably up to 25% by weight, of one or moremonomers from the following group: ethylene, α-olefins having from 3 to18 carbon atoms (e.g., propylene, butylene), styrene, vinyltoluene,vinylxylene, halogenated, unsaturated, aliphatic hydrocarbons (e.g.,vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidenefluoride) and/or

b) up to 25% by weight, preferably between 1 and 5% by weight, of one ormore monomers from the following group: α,β-unsaturated acids (e.g.,acrylic acid, methacrylic acid), esters of α,β-unsaturated acids withprimary or secondary, saturated, monohydric alcohols having from 1 to 18carbon atoms (e.g., methanol, ethanol, propanol, butanol,2-ethylhexanol, cycloaliphatic alcohols, and relatively long-chain fattyalcohols), α,β-unsaturated dicarboxylic acids (e.g., maleic acid,fumaric acid, itaconic acid, citraconic acid), monoesters and/ordiesters of α,β-unsaturated dicarboxylic acids with saturated,monohydric, aliphatic alcohols having from 1 to 18 carbon atoms and/or

c) up to 10% by weight, preferably up 2% by weight, of one or moremonomers from the group consisting of polyethylenically unsaturatedmonomers, such as diallyl phthalate, diallyl maleate, triallylcyanurate, tetraallyloxyethane, divinylbenzene, butan-1,4-dioldimethacrylate, triethylene glycol dimethacrylate, divinyl adipate,allyl (meth)acrylate, vinyl crotonate, methylenebisacrylamide,hexanediol diacrylate, pentaerythritol diacrylate, trimethylolpropanetriacrylate and/or

d) up to 15% by weight, preferably up to 10% by weight, of one or morenitrogen-containing monomers containing N-functional groups, such as(meth)acrylamide, allyl carbamate, acrylonitrile,N-methylol(meth)acrylamide, N-methylolallylcarbamate, N-methylol esters,N-methylol alkyl ethers or Mannich bases of N-methylol(meth)acrylamideor N-methylolallylcarbamate, acrylamidoglycolic acid, methylacrylamidomethoxyacetate, N-(2,2-dimethoxy-1 -hydroxyethyl)acrylamide,N-dimethylaminopropyl(meth)-acrylamide, N-methyl(meth)acrylamide,N-butyl(meth)acrylamide, N-cyclohexyl(meth)acrylamide,N-dodecyl(meth)acrylamide, N-benzyl(meth)acrylamide,p-hydroxyphenyl(meth)acrylamide,N-(3-hydroxy-2,2-dimethylpropyl)methacrylamide, ethylimidazolidonylmethacrylate, N-vinylformamide, N-vinylpyrrolidone anchor

e) up to 25% by weight, preferably up to 15% by weight, of one or moremonomers from the group consisting of hydroxy-functional monomers, suchas hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate or theadducts thereof with ethylene oxide or propylene oxide, and/or

f) up to 10% by weight, preferably up to 5% by weight, of one or moremonomers from the group consisting of monomers which areself-crosslinking and/or crosslinkable by way of carbonyl groups, suchas diacetoneacrylamide, allyl acetoacetate, vinyl acetoacetate andacetoacetoxyethyl (meth)acrylate, for example.

Examples of suitable polymeric protective colloids include polyvinylalcohols, copolymeric polyvinyl alcohols which carry carboxyl monomers,-ethylene and/or 1 -methylvinyl alcohol units, polymer-analogousreaction products of polyvinyl alcohols, examples being those withdiketene, etherified cellulose derivatives, such ashydroxyethylcellulose and carboxymethylcellulose, polyvinylpyrrolidone,polycarboxylic acids, such as polyacrylic acid, and/or copolymers, ofmaleic acid or of maleic anhydride with ethylenically unsaturatedcompounds, such as methyl vinyl ether, isobutylene or styrene, forexample. Of preferred suitability as a protective colloid is polyvinylalcohol with a degree of hydrolysis of from 60 to 100 mol %, with,particular preference having a degree of hydrolysis of from 70 to 98 mol%, and having viscosities of the 4% strength by weight aqueous solutionsof from 2 to 70 mPas at 20° C.

The fraction of the polymeric protective colloids, based on the solidsfraction, is preferably 1 to 25% by weight and with particularpreference from 2 to 10% by weight.

Where appropriate, the adhesive dispersion may comprise nonionic and/orionic emulsifiers, additives and/or auxiliaries. The fraction ofemulsifiers, based on the polymer, is preferably up to 2% by weight.Examples of additives are film forming auxiliarities for lowering theMFT, plasticizers, defoamers, fillers, and preservatives. Auxiliarieswhich can be used include, for example, complexing agents based onpolydentate ligands, such as ethylenediaminetetraacetic acid, forexample, which form complexes with the water-soluble cations of themetal salts used and thereby improve the color constancy of thegluelines.

Suitable compounds which can be complexed with the polymeric protectivecolloids include water-soluble metal salts and salts and acids withoxoanions. Metal salts possessing preferred suitability are acidic metalsalts with polyvalent complexible cations, such as are set out, forexample, in DE-B-22 61 402, in DE-C-26 20 738, and in DE-A-39 42 628.Particularly suitable compounds are the water-soluble metal salts ofAl(III) and Zr(IV), and especially aluminum chloride, aluminum nitrate,and zirconium oxychloride. Salts and acids with oxo anions that are ofpreferred suitability include those whose oxo anions are able to bindpolyanions. Particularly suitable are borates and phosphates, andespecially free boric acid and free phosphoric acid.

The glyoxal derivatives comprise adducts of glyoxal with S, O and/or Nnucleophiles. Suitable adducts of S-nucleophiles are, for example, thebisulfite adducts, preferably those of sodium hydrogen sulfite orpotassium hydrogen sulfite. Examples of suitable O-nucleophiles arealiphatic (C₁ to C₂₀) monoalcohols. Of preferred suitability are (C₁ toC₁₂) monoalcohols, such as methanol and ethanol, for example. Likewisesuitable as O-nucleophiles are polyhydric alcohols, such as ethyleneglycol, 1,2-propylene glycol, and 1,3-propylene glycol, for example. Asan example of an adduct, mention may be made of2,3-dihydroxy-1,4-dioxane. Examples of suitable N-nucleophiles includealiphatic monoamines, amides, and urea and cyclic ureas, such asethyleneurea, for example. As an example of an adduct, mention may bemade of 3,4-dihydroxyethyleneurea.

In the context of the invention, with regard to the masking of theglyoxal, hybrid forms of the abovementioned masking possibilities are ofcourse also permissible.

The adhesive dispersions of the invention contain, based on the solidmatter of the adhesive dispersion, preferably from 0.001 to 10% byweight, with particular preference from 0.01 to 5% by weight, and inparticular from 0.1 to 2% by weight, of glyoxal derivatives.

Examples of polyaldehydes having at least 3 carbon atoms aremalonaldehyde, succinaldehyde, glutaraldehyde, 2-hydroxyglutaraldehyde,β-methylglutaraldehyde, pimelaldehyd, suberaldehyde, malealdehyde andfumaraldehyde, sebacaldehyde, malaldehyde, phthalaldehyde,isophthalaldehyde, terephthalaldehyde, and ring-substituted aromaticaldehydes.

The derivatives of the polyaldehydes having at least 3 carbon atomscomprise adducts of the polyaldehydes with S, O and/or N nucleophiles.Preferred adducts are the bisulfite adducts. Particular preference isgiven to the glutaraldehyde bisalkali metal hydrogen sulfites. Preferredcounterions of the bisulfite adducts are lithium, sodium, potassium,magnesium, calcium, aluminum, and ammonium ions and/or substitutedammonium ions.

Further inventively suitable derivatives of the polyaldehydes having atleast 3 carbon atoms are their open-chain acetals with aliphatic(C₁-C₂₀) monoalcohols, preferably (C₁ to C₁₂) monoalcohols, especiallymethanol and ethanol, and their cyclic acetals with alcohols having afunctionality of at least two, preferably ethylene glycol, 1,2-propyleneglycol, and 1,3-propylene glycol. By way of example, mention may be madeof chloromalonaldehyde bisdiethyl acetal, succinaldehyde mono- andbisdimethyl acetal, succinaldehyde bisdiethylacetal,2-bromosuccinaldehyde bisdimethyl acetal, oximinosuccinaldehydebisdimethyl acetal, and the bisdimethyl and bisdiethyl acetals ofmalealdehyde. This group further embraces the intramolecular cyclicacetals of succinaldehyde and glutaraldehyde, such as2,5-dimethoxytetrahydrofuran, 2,5-diethoxytetrahydrofuran, and2,6-dimethoxy-tetrahydro-2H-pyran and 2,6-diethoxytetrahydro-2H-pyran.Particularly suitable compounds from this group are the bisdimethyl andbisdiethyl acetals of malonaldehyde and glutaraldehyde.

Further suitable derivatives of the polyaldehydes having a least 3carbon atoms are their enol ethers, enol esters, acylates, and mixedacylate ethers. Among these compounds, there exist those which containaldehyde groups which for constitutional reasons are predominantly inthe enol form, an example being hydroxypyruvaldehyde (reductone). These,and also reaction products of the enols in which the residual aldehydegroups not present in the enol form may also have been masked, arelikewise suitable derivatives.

Derivatives of the polyaldehydes having at least 3 carbon atoms that arelikewise suitable in accordance with the invention are the cleavablereaction products of the polyaldehydes with nitrogen compounds. Thesederivatives include the oximes, oxime esters, oxime ethers, imines(Schiff bases), enamines, aminals, hydrazones, semicarbazones, anils,diurethanes and enamine urethanes of polyfunctional aldehydes. Exampleswhich may be mentioned include glutaraldehyde dioxime, phthalaldehydemonoxime and dioxime, phthalaldehyde oxime semicarbazone,isophthalaldoxime, terephthalaldoxime, terephthalaldehyde dihydrazone,and the anils of malonaldehyde, succinaldehyde, and glutaraldehyde.

In the context of the invention, with regard to the masking of thepolyaldehydes having at least 3 carbon atoms, hybrid forms of theabovementioned masking possibilities are of course also permissible.

The adhesive dispersions of the invention contain, based on the solidmatter of the adhesive dispersion, preferably from 0.001 to 10% byweight, with particular preference from 0.01 to 5% by weight, and inparticular from 0.1 to 2% by weight, of derivatives of the polyaldehydeshaving at least 3 carbon atoms.

The adhesive dispersions of the invention possess a pH at which thederivatives of the polyaldehydes having at least 3 carbon atoms and,where appropriate, the derivatives of glyoxal are hydrolyzed and thealdehyde groups are controlledly released. This pH range is situatedpreferably between 2 and 6, with particular preference between 2.5 and4. In order to adjust the pH, organic and/or inorganic Lewis andBrönsted acids are added where appropriate. Brönsted acids of preferredsuitability have a pK_(a) of <2.5, such as, for example, phosphoricacid, hydrochloric acid, sulfuric acid, nitric acid, perchloric acid,and p-toluenesulfonic acid. The particularly preferred Brönsted acid isphosphoric acid. Lewis acids of preferred suitability are the acidicsalts of complexible metal ions. Particularly preferred Lewis acids arealuminum chloride, aluminum nitrate, and zirconium oxychloride.

In two-component systems, the adhesive is preferably activated by addingthe acidic complexible compounds.

The solids content of the adhesive dispersion of the invention ispreferably from 20 to 65% by weight, with particular preference from 30to 60% by weight.

The present invention also provides a process for preparing thedispersion adhesives of the invention, wherein a mixture is prepared inthe form of a formulated polyvinyl ester dispersion comprising asconstituents at least

a) one homopolymeric and/or copolymeric polyvinyl ester,

b) one polymeric protective colloid,

c) one compound which can be complexed with the polymeric protectivecolloids, and

d) two, at least partly masked polyaldehydes which release aldehydegroups again in acidic media, in which at least one masked polyaldehydeis a glyoxal derivative and at least one other masked polyaldehyde is aderivative of a polyaldehyde having at least 3 carbon atoms, andsubsequently, where necessary, adjusting the pH by adding Lewis and/orBrönsted acids.

The preparation of the adhesive of the invention may comprise thepreparation of polyvinyl ester dispersions which comprise theconstituent a), a portion, preferably the entirety, of the polymericprotective colloids b) and, where appropriate, emulsifiers, acids suchas filming assistants, etc., and/or auxiliaries.

The polyvinyl ester dispersions may be prepared by means of customarycontinuous or batchwise processes of free-radical emulsionpolymerization. In these processes, water-soluble and/or oil-solubleinitiator systems such as peroxodisulfates, azo compounds, hydrogenperoxide, organic hydroperoxides or dibenzoyl peroxide are employed.These may be used either by themselves or in combination with reducingcompounds such as Fe(II) salts, sodium pyrosulfite, sodium hydrogensulfite, sodium sulfite, sodium dithionite, sodiumformaldehyde-sulfoxylate, ascorbic acid, as a redox catalyst system. Thepolymeric protective colloids and, where appropriate, the emulsifiers,additives and/or auxiliaries may be added before, during or after thepolymerization.

In one preferred embodiment for a two-component or multicomponentadhesive, as a first component first of all a mixture is preparedcomprising the constituents a), b), c), and, where appropriate,emulsifiers, additives and/or auxiliaries. Subsequently the maskedpolyaldehydes d), comprising the glyoxal derivatives and the derivatesof the polyaldehydes having at least 3 carbon atoms, are added togetheror separately to the mixture.

In one variant of this embodiment, first of all a mixture is preparedcomprising the constituents a), b), c), the glyoxal derivatives, and,where appropriate, emulsifiers, additives and/or auxiliaries.Subsequently the derivatives of the polyaldehydes having at least 3carbon atoms are added as a further component to the mixture.

In one further preferred embodiment for a two-component ormulticomponent adhesive, first of all a mixture is prepared comprisingthe constituents a), b), d), and, where appropriate, emulsifiers,additives and/or auxiliaries. Subsequently the mixture is activated byadding the compounds c) which can be complexed with the polymericprotective colloids. Activating compounds used are preferably aqueoussolutions containing aluminum chloride, aluminum nitrate and/orzirconium oxychloride. The mixture ought to possess as far as possible aneutral pH, but at least a pH of 6, before the complexing compounds areadded, since in that case there is only very slow hydrolysis, if any, ofthe masked polyaldehydes, and this enhances the service life of theunactivated adhesive. For this purpose, the pH of the mixture may alsobe adjusted subsequently by adding customary neutralizing agents.

The glyoxal derivatives and the derivatives of the polyaldehydes havingat least 3 carbon atoms may be added as solids or in the form solutions.Examples of suitable solutions include aqueous solutions or solutions inaliphatic alcohols. The addition lakes place preferably in the form of aconcentrated, aqueous solution, since in that case the drop in viscosityin the dispersion is minimized.

The preparation of the activated adhesive system may of course also befollowed, where necessary, by further formulation—for example, by theaddition of auxiliaries, such as defoamers, or the addition of furtherpolymeric protective colloids, such as polyvinyl alcohol, etc., in orderto prolong the open time. These procedures are known in principle to theskilled worker.

The invention further provides for the use of the dispersion adhesivesof the invention for adhesively bonding porous and semiporoussubstrates. Preferred substrates are wood, paper, cardboard, corrugatedcardboard, foam materials, cement, leather, textiles or laminates.

The adhesive preparations of the invention are particularly suitable asadhesives for cellulosic substrates such as wood and paper. Theadhesives are suitable for manual or machine application, and also,owing to the color neutrality of the bonds, particularly forapplications where the bond lines are cured by means of high-frequencyalternating fields. One specific field of application is the productionof window frames, and also veneer gluing.

More specific applications of the adhesive dispersions of the inventionlie in adhesives and binders for the architectural, domestic, andtextile sectors, such as flooring, wall, and ceiling adhesives,furniture film adhesives and carpet backing adhesives, binders for woodfiberboard and reconstituted leather, binders for insulating materialsmade from paper fibers or polymer fibers, binders for acid-resistantminerals in architectural dispersions, and binders for textiles andnonwovens. Use as an adhesive and/or binder in textile printing and as atextile finish is likewise possible.

In comparison with the adhesive dispersions described in the prior art,the adhesive dispersions of the invention have prolonged pot lives, orslower increases in viscosity, with improved color constancy and acomparably high level of glueline. water resistance. The adhesive bondssatisfy the requirements of the test standard DIN EN 204 forclassification in at least durability class D2, preferably durabilityclass D3, and in particular durability class D4.

It should also be emphasized that the dispersion adhesives of theinvention are, advantageously, systems which are isocyanate-free and toa substantial extent also formaldehyde-free. Especially in dispersionswhich include constituents which give off formaldehyde, the particularlypreferred hydrogen sulfite adducts of glyoxal and also the polyaldehydeshaving at least 3 carbon atoms afford the further advantage, moreover,that the hydrogen sulfite released on crosslinking acts as aformaldehyde scavenger and so markedly decreases the concentration offree formaldehyde in the adhesives or binders.

Test Methods Used:

1. Determination of the Pot Life:

In the absence of numerical viscosity figures, this means a time periodwithin which the adhesive dispersion in the formulated end form (withmetal salt and crosslinking agent) were still reliably flowable with aviscosity (to be checked daily) of ≦40 Pa·s according to Brookfield RVT6/20.

2. Determination of the Bond Strengths:

The bond strengths (tensile strengths) were determined on beech woodtest specimens following boiling water treatment in accordance with thetest standard DIN EN 204/D4. The test specimens were produced inaccordance with the procedure of DIN EN 205. Gluing and testing wereconducted while observing the following parameters:

Maturation time following 2 hours addition of hardener Glue application150 ± 20 g/m², both sides Open waiting time 3 minutes Closed waitingtime 2 hours Pressing time 2 hours Pressing pressure 0.7 ± 0.1 N/mm²Number of test specimens 20 per test series Testing of the storageseries in 7 days of standard conditions accordance with DIN EN 204 D4/5(23 ± 2° C. and 50 ± 5% relative humidity) 6 hours in boiling water 2hours in cold water Test temperature 23 ± 2° C. Advance rate 50 mm/min

Classification in durability class D4/5 was made for a bond strength(tensile strength) of at least 4 N/mm².

3. Determination of the discoloration on oak

The adhesive dispersions were applied to oak in a wet application of 800μm using a box-type coating bar and then were placed in this form in aheated drying oven at 90° C. After 45 minutes, the dried films wereremoved and the discoloration assessed visually.

The examples below serve to illustrate the invention without restrictingit. The parts and percentages indicated in the examples relate to theweight unless noted otherwise. The comparative adhesives were adhesivesin acordance with EP-B-0 686 682.

EXAMPLE 1 Preparation of an Inventive Adhesive 1 and of a ComparativeAdhesive 1

In a glass stirred tank reactor with anchor stirrer, equipped with feedfacilities, reflux condenser, jacket heating and jacket cooling, apolyvinyl acetate homopolymer dispersion containing 100 parts ofpolyvinyl acetate was prepared using 5 parts of Mowiol® 18-88 (ClariantGmbH, partially hydrolyzed polyvinyl alcohol with degree of hydrolysisof 88 mol %) as protective colloid and 0.1 part of hydrogen peroxide asinitiator. A metering technique was employed, with 4.2 parts of vinylacetate being introduced as initial charge and 95.8 parts of vinylacetate metered in over the course of 3 hours at a polymerizationtemperature of 70 to 74° C. After the end of polymerization, 0.17 partof sodium acetate was added. This gave a coagulum-free dispersion havinga pH of 3.8, a solids content of 50% by weight, a monomeric vinylacetate content of 0.4%, and a viscosity of 48.8 Pa·s (measurementsystem: Brookfield 6/20, 23° C.). Thereafter, 2% of butyl diglycolacetate was added to the dispersion in order to lower the MFT, and 5% ofa saturated solution of aluminum chloride hexahydrate was added to thedispersion.

In case of the inventive adhesive 1, the above dispersion wassubsequently admixed with aqueous solutions of commercial glutaraldehydebis-sodium hydrogen sulfite (GABNA) and commercial glyoxal bis-sodiumhydrogen sulfite monohydrate (GLYBNA). In the case of the comparativeadhesive 1, the dispersion was subsequently admixed only with an aqueoussolution of commercial glutaraldehyde bis-sodium hydrogen sulfite(GABNA). The initial viscosity of the two adhesives was in each case 7Pa·s (Brookfield 6/20, 23° C.). Table 1 indicates the composition of theadhesives. Likewise indicated in Table 1 are the pot lives and the bondstrengths of the adhesives in accordance with DIN EN 204.

TABLE 1 Compositions, pot lives and bond strengths of the inventiveadhesive 1 and of the comparative adhesive 1 in accordance with DIN EN204 Inventive Comparative adhesive 1 adhesive 1 (as per EP-B-0 686 682)Parts of Dispersion 100 100 Parts of GABNA 0.5 0.5 Parts of GLYBNA 0.5 —Parts of water 4 4 Pot life/days >3 days 1 day D4/5 N/mm² 4.2 4.0

Table 1 shows that the inventive adhesive 1, with a hot water resistancecomparable with that of the comparative adhesive 1, has a markedlyprolonged pot life.

EXAMPLE 2 Preparation of an Inventive Adhesive 2 and of a ComparativeAdhesive 2

100 parts of Mowilith® D, approximately 50% (polyvinylalcohol-stabilized polyvinyl acetate homopolymer dispersion, ClariantGmbH) were admixed with 2.2 parts of a saturated solution of aluminumchloride hexahydrate, giving a pH of 3. To prepare the inventiveadhesive 2, aqueous solutions of commercial glutaraldehyde bis-sodiumhydrogen sulfite (GABNA) and commercial glyoxal bis-sodium hydrogensulfite monohydrate (GLYBNA) were subsequently added. To prepare thecomparative adhesive 2, only an aqueous solution of commercialglutaraldehyde bis-sodium hydrogen sulfite (GABNA) was added. Bothadhesives possessed an initial viscosity of 7 Pa·s (Brookfield 6/20, 23°C.). The compositions of the inventive adhesive 2 and the comparativeadhesive 2 are indicated in Table 2. The inventive adhesive 2 and thecomparative adhesive 2 were subjected in accordance with DIN EN 204 to adetermination of the bond strength, to a determination of thediscoloration on oak, and to the determination of the viscosity as afunction of time. The results are set out in Table 2 and Table 3.

TABLE 2 Compositions, pot lives, bond strengths to DIN EN 204, anddiscoloration on oak of the inventive adhesive 2 and of the comparativeadhesive 2 Inventive Comparative adhesive 2 adhesive 2 (as per EP-B-0686 682) Parts of Dispersion 102.2 102.2 GABNA 0.67 0.67 GLYBNA 0.5 —Water 6.25 6.25 D4/5 N/mm² 4.2 4.3 Discoloration on oak almost colorlesslight brown discoloration

TABLE 3 Viscosity change (measurement system Brookfield 6/20) of theinventive adhesive 2 and of the comparative adhesive 2 as a function oftime at 23° C. Viscosity of the Viscosity of the comparative Timeinventive adhesive 2 adhesive 2 (as per EP-B-0 686 (days) (Pa*s) 682)(Pa*s) 0 7.1 7.1 1 7.4 9.7 2 9.1 14.7 3 10.8 20.0 5 12.6 28.6 7 22.042.0

Example 2 shows that, as compared with the comparative adhesive 2, theinventive adhesive 2 has a comparably high level of hot water resistancewhile exhibiting a slower viscosity increase and more favorablediscoloration characteristics on oak.

What is claimed is:
 1. An aqueous dispersion adhesive comprising: a) atleast one homopolymeric and/or copolymeric polyvinyl ester, b) at leastone polymeric protective colloid, c) at least one water-soluble compoundwhich can be complexed with the at least one polymeric protectivecolloid, and d) at least two, at least partly masked polyaldehydes whichrelease aldehyde groups in acidic media, wherein at least one maskedpolyaldehyde is a glyoxal derivative and at least one other maskedpolyaldehyde is a derivative of a polyaldehyde having at least 3 carbonatoms.
 2. The dispersion adhesive as claimed in claim 1, wherein thehomopolymeric and copolymeric polyvinyl esters comprise as monomer unitsvinyl acetate, vinyl formate, vinyl propionate, vinyl isobutyrate, vinylpivalate, vinyl 2-ethylhexanoate, vinyl esters of saturated, branchedmonocarboxylic acids having 9 to 10 carbon atoms in the acid radical,vinyl esters of relatively long-chain, saturated or unsaturated fattyacids, vinyl esters of benzoic acid and/or vinyl esters of substitutedderivatives of benzoic acid.
 3. The dispersion adhesive as claimed inclaim 1, wherein the homopolymeric and copolymeric polyvinyl esterscomprise vinyl acetate as monomer units.
 4. The dispersion adhesive asclaimed in claim 1, wherein the weight fraction of vinyl ester(s) in thecopolymeric polyvinyl esters is at least 50% by weight.
 5. Thedispersion adhesive as claimed in claim 1, wherein the copolymericpolyvinyl esters comprise as monomer units a) up to 50% by weight of oneor more monomers selected from the group consisting of: ethylene,α-olefins having from 3 to 18 carbon atoms, styrene, vinyltoluene,vinylxylene, halogenated, unsaturated, and aliphatic hydrocarbons and/orb) up to 25% by weight of one or more monomers selected from the groupconsisting of: α,β-unsaturated acids, esters of α,βunsaturated acidswith primary or secondary, saturated, monohydric alcohols having from 1to 18 carbon atoms, α,β-unsaturated dicarboxylic acids, and monoestersand/or diesters of α,β-unsaturated dicarboxylic acids with saturated,monohydric, aliphatic alcohols having from 1 to 18 carbon atoms and/orc) up to 10% by weight of one or more monomers from polyethylenicallyunsaturated monomers and/or d) up to 15% by weight of one or morenitrogen-containing monomers containing N-functional groups and/or e) upto 25% by weight of one or more monomers containing hydroxy-functionalgroups and/or f) up to 10% by weight of one or more monomers selectedfrom the group consisting of monomers which are self-crosslinking andmonomers which are crosslinkable by way of carbonyl groups.
 6. Thedispersion adhesive as claimed in claim 1, wherein the at least onepolymeric protective colloid is selected from the group consisting ofpolyvinyl alcohols, copolymeric polyvinyl alcohols which carry carboxylmonomers, -ethylene and/or 1methylvinyl alcohol units, polymer-analogousreaction products of polyvinyl alcohols, etherified cellulosederivatives, polyvinylpyrrolidone, polycarboxylic acids and copolymersof maleic acid or of maleic anhydride with ethylenically unsaturatedcompounds.
 7. The dispersion adhesive as claimed in claim 1, containingfrom 1 to 25% by weight, based on the solids fraction, of at least onepolymeric protective colloid.
 8. The dispersion adhesive as claimed inclaim 1, wherein the at least one water soluble compound compounds whichcan be complexed with the polymeric protective colloid is selected fromthe group consisting of water-soluble metal salts, salts with oxoanionsand acids with oxoanions.
 9. The dispersion adhesive as claimed in claim8, wherein the water-soluble metal salts are salts of Al(III) and Zr(IV)and wherein the oxoanions are borates and phosphates.
 10. The dispersionadhesive as claimed in claim 1, wherein the glyoxal derivative is anadduct of glyoxal with S, O and/or N nucleophiles.
 11. The dispersionadhesive as claimed in claim 10, wherein the S nucleophiles are adductswith sodium hydrogen sulfite and/or potassium hydrogen sulfite, whereinthe O nucleophiles are adducts with aliphatic (C₁ to C₂₀) monoalcoholsand/or monohydric alcohols, and wherein the N nucleophiles are aliphaticmonoamines, amides, urea and/or cyclic ureas.
 12. The dispersionadhesive as claimed in claim 1, containing from 0.001 to 10% by weight,based on the solid matter, of the glyoxal derivative.
 13. The dispersionadhesive as claimed in claim 1, wherein the derivative of a polyaldehydehaving at least 3 carbon atoms is selected from the group consisting ofmalonaldehyde, succinaldehyde, glutaraldehyde, 2-hydroxyglutaraldehyde,βmethylglutaraldehyde, pimelaldehyd, suberaldehyde, malealdehyde andfumaraldehyde, sebacaldehyde, malaldehyde, phthalaldehyde,isophthalaldehyde, terephthalaldehyde, and ring-substituted derivativesof aromatic aldehydes.
 14. The dispersion adhesive as claimed in claim1, wherein the derivative of a polyaldehyde having at least 3 carbonatoms comprises adducts of polyaldehydes with S, O and/or Nnucleophiles.
 15. The dispersion adhesive as claimed in claim 14,wherein the derivative of a polyaldehyde having at least 3 carbon atomsis selected from the group consisting of bisulfite adducts, open-chainacetals, cyclic acetals, enol ethers, enol esters, acylates, mixedacylate ethers, oximes, oxime esters, oxime ethers, imines (Schiffbases), enamines, aminals, hydrazones, semicarbazones, anils,diurethanes and enamine urethanes.
 16. The dispersion adhesive asclaimed in claim 15, wherein the bisulfite adducts are theglutaraldehyde bis-alkali metal hydrogen sulfites.
 17. The dispersionadhesive as claimed in claim 1, containing from 0.001 to 10% by weight,based on the solid matter, of the derivative of a polyaldehyde having atleast 3 carbon atoms.
 18. The dispersion adhesive as claimed in claim 1,possessing a pH in the range from 2 to
 6. 19. A window frame adhesivecomprising the dispersion adhesive as claimed in claim
 1. 20. A binderfor textiles and nonwovens comprising the dispersion adhesive as claimedin claim
 1. 21. A veneer glue comprising the dispersion adhesive asclaimed in claim
 1. 22. A bonding composition for bonding substratescomprising the dispersion adhesive as claimed in claim
 1. 23. A processfor preparing a dispersion adhesive comprising the step of preparing amixture in the form of a formulated polyvinyl ester dispersion, whereinthe formulated polyvinyl ester dispersion includes: a) at least onehomopolymeric and/or copolymeric polyvinyl ester, b) at least onepolymeric protective colloid, c) at least one compound which can becomplexed with the polymeric protective colloid, and d) at least two, atleast partly masked polyaldehydes which release aldehyde groups again inacidic media, in which at least one masked polyaldehyde is a glyoxalderivative and at least one other masked polyaldehyde is a derivative ofa polyaldehyde having at least 3 carbon atoms.
 24. The process asclaimed in claim 23, wherein the preparing step further comprises mixingconstituents a), b), and c), and subsequently adding constituent d) toconstituents a), b), and c).
 25. The process as claimed in claim 23,wherein the preparing step further comprises mixing the constituents a,b), c) and, and the glyoxal derivative, and subsequently adding thederivative of the polyaldehyde having at least 3 carbon atoms to theconstituents a), b), c), and the glyoxal derivative.
 26. The process asclaimed in claim 23, wherein the preparing step further comprises mixingthe constituents a), b), and d), and subsequently activating thepolyvinyl ester dispersion by adding constituent c) to constituents a),b), and d).
 27. The process as claimed in claim 23, further comprisingthe step of adjusting the pH of the mixture by adding Lewis and/orBrönsted acids.